/Engine/Source/Runtime/Engine/Classes/Sound/SampleBufferIO.h
This is a blocking call that will return the SoundWave generated from InSampleBuffer. Optionally, if you're using the editor, you can also write the resulting soundwave out to the content browser using the FileName and FilePath parameters.
[USoundWave](API\Runtime\Engine\Sound\USoundWave) * SynchronouslyWriteSoundWave ( const [TSampleBuffer](API\Runtime\SignalProcessing\TSampleBuffer)<> & InSampleBuffer, const [FString](API\Runtime\Core\Containers\FString) * FileName, const [FString](API\Runtime\Core\Containers\FString) * FilePath )